Based on a movement of a movable object, such as a vehicle, a navigation apparatus may learn of a new road, which is not registered in a ready-made map data. Such a navigation apparatus is conventionally disclosed in, for example, Japanese Patent Laid-Open No. H06-88733 (JP '733) and Japanese Patent Laid-Open No. 2006-125883 (JP '883). The road learning function is a function that learns a new road not registered in the map data, by generating a new road (i.e., a learned road) and storing it, based on a trace of the vehicle's movements from a point where a current vehicle position departed from an existing road of the map data to a point where the current vehicle position returned to the existing road.
When the learned road is used for route guidance, the learned road may be used for route guidance, depending on the reliability of the learned road. The examples of credibility problem are described in the following.
On way to a destination, the user may go to an intervening destination, such as a store, which is close to an intersection or a branch point of a road (e.g., a rotary, a junction, etc.). In such case, the ramp road (i.e., entrance) not on the road (i.e., not on the public road) may be counted or considered as part of the branch and may be stored as a learned road. The learned road may later be used as a guidance route by the navigation apparatus when the vehicle travels the road that passes the branch point or the branch point associated with the learned road, even though the learned road is not a public road. Therefore, the route guidance may be erroneous and problematic for such a branch point, since the actual road shape of such guidance point may not match the provided route guidance.
In other words, the progress direction shown by the route guidance at the branch is provided for the user as a connection direction of an exit route from the branch, which is to be traveled per the guidance route, and further as a relative positioning with other road(s) exiting from that branch.
For instance, if the guidance route at a branch is a right turn toward a right exit route and there is another right road exiting from the same branch, the two right roads from the same branch are respectively distinguished as a far-right road and a near-right road, for example, in the route guidance regarding the progress direction. That is, an absolute direction and the relative positioning of the roads are combined in the route guidance.
In case that the learned road connected to the branch is an actual public road, the route guidance at the branch in consideration of such learned road is not a problem, in terms of the progress direction shown by the route guidance. However, in case that the learned road is not a public road, which may be a ramp road into a facility site or an entrance road into a parking, the route guidance at the branch in consideration of such learned road is problematic, causing uncertainty in the route guidance because the route guidance and the branch shape may not be coinciding.
Therefore, for example, an exit route from a branch, which should be simply guided as “a right direction,” may be mis-guided as “a near-right direction” in consideration of the learned road that is a ramp road existing in the right direction from the same branch.
In the prior art, distinction between learned road links and existing road links of the map data is not provided. Thus the reliability-considered route guidance based on the reliability of the learned road cannot be performed.